The present invention relates to the identification of fasteners with bar codes and the measurement of load in fasteners using ultrasonic load measurement methods.
Techniques have been developed for performing direct load measurements in fasteners utilizing ultrasonic transducers which are removably, or preferably permanently attached to the fasteners. Examples of such techniques can be found, for example, in U.S. Pat. No. 6,990,866 (Kibblewhite); U.S. Pat. No. 6,009,380 (Vecchio et al.); U.S. Pat. No. 5,220,839 (Kibblewhite); U.S. Pat. No. 5,018,988 (Kibblewhite et al.); U.S. Pat. No. 4,899,591 (Kibblewhite); and U.S. Pat. No. 4,846,001 (Kibblewhite), each of which is incorporated by reference as if fully set forth herein. It has been found that such techniques make it possible to directly control the installation load of various different types of fasteners using all types of assembly tools, including impact and impulse tools.
The above-referenced U.S. Pat. No. 6,990,866 discloses a load indicating member with a permanent identifying mark which can be read and used to determine ultrasonic measurement parameters specific to the load indicating member. This provides more precise and more reliable load measurements by compensating for differences resulting from manufacturing variations in individual load indicating members.
In one disclosed embodiment, a load indicating member has an ultrasonic transducer permanently mechanically, electrically and acoustically attached to one end of the load indicating member such that the load indicating member functions as a first electrode. The ultrasonic transducer comprises a piezoelectric element, adjacent to the end surface of the load indicating member, and an electrically conductive layer adjacent to the piezoelectric element functions as a second electrode. A high-density, two-dimensional, optically-read bar code is permanently marked on the surface of the electrode. In another disclosed embodiment, the bar code is used to store all of the ultrasonic parameters specific to that load indicating member which are required to make precise, reliable load measurements. In another disclosed embodiment, the bar code stores a unique identification of the load indicating member, which is used to retrieve from a database the ultrasonic parameters specific to that load indicating member which are required to make precise, reliable load measurements.
Also disclosed is a method of measuring the load in a load indicating member which includes the steps of reading the bar code with an optical reader, determining the ultrasonic measurement parameters, making pulse-echo time-of-flight ultrasonic wave measurements, and calculating the precise load.
In certain situations, however, it is not possible to read the bar code with a conventional bar code reader. One example of such a situation occurs after a fastener is installed, and other components of the assembly restrict the access of the bar code reader. Another example is during the installation of the fastener, when it is desirable to identify the bolt immediately prior to tightening with an assembly tool. In this situation, it is desirable to identify and tighten the fastener in a single operation to minimize fastener installation time and to eliminate operator errors. For example, such operator errors can occur in multiple bolt joints when one fastener is identified and then a different fastener is tightened.